At the top of the window in which you are viewing c:\program files\EA GAMES\ The Sims2 Free Time\TSBin there is a toolbar with a number of options - File, Edit, View, Favourites, Tools and Help. Click on Tools and then Folder Options. Select the View tab and go to the line where it says 'hide known file extensions'. Uncheck that box. Hit ok.
Remember to back up first!